1. Technical Field
The invention relates to an impeller, and more particularly, the invention relates to an impeller which has two kinds of alternate blades.
2. Description of the Related Art
In a conventional electrical system, since its internal electronic element is a large heat source, and the performance of the internal electronic element degrades with the increasing of the temperature thereof, the heat generated thereby has to be quickly removed so as to keep the internal electronic element's regular performance. Therefore, a fan generating airflow is commonly used to achieve the objective of rapidly dissipating heat.
Please refer to FIGS. 1 and 2. The conventional impeller 10 includes a hub 11 and a plurality of blades 12 circumferentially disposed around the hub 11. When the impeller 10 rotates along a rotating direction R1, an air-pressure is produced by the blades 12 so as to generate airflow 13 for heat dissipation.
When the performance of an electronic element is enhanced, the heat generated by the electronic element is also greatly increased accordingly. For better heat dissipation, the rotational speed of the conventional fan has to be greatly increased. However, when the rotational speed of the impeller 10 is increased, an unpleasant noise gets louder due to turbulence airflow occurring between the blades 12.
Thus, it is a dilemma for a user. If the rotational speed is decreased, efficiency of heat dissipation degrades. If the rotational speed is increased, the noise produced by the fan becomes louder.